Abstract: Drought stress is considered as a limiting factor for plant productions therefore, many compounds have been applied to minimize the harmful effects of stress. In this study, the effect of paclobutrazol, a triazole growth regulator, on morphological and biochemical parameters of Brassica napus L. under in vitro drought stress was investigated. First, the seeds of B. napus L. were sterilized and then were cultured in MS medium supplemented with mannitol at percentages of 0, 4 and 8 )various levels of drought) and 0, 10 and 20 ppm paclobutrazol. Also, B. napus stem explants were cultured in MS medium containing rooting and callogenesis hormones with mannitol (0, 4, 8%) and paclobutrazol (0, 10 ppm). After 4 weeks, results showed stem and root length, stem and root dry weight, chlorophyll a, total chlorophyll, carotenoids, rooting and callogenesis percentage and callus fresh weights significantly decreased but lipid peroxidation, reducing sugar and proline increased in seedlings which were under drought stress. Decreased peroxidation of lipids and increased the root length, stem and root weight, reducing sugars, proline, photosynthetic pigments and protein of the seedlings which were treated with both paclobutrazol and drought stress were also observed, which was probably the indication of reduction of the damage caused by stress in these seedlings. Therefore paclobutrazol especially in concentrations of 10 ppm was more effective in relieving stress damages caused by drought stress in B. napus L.

Keywords: Paclobutrazol, Drought stress, In vitro culture, Brassica napus L.

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